Generally, bicycle speed change device are well-known, in which, as shown in FIG. 6, a front derailleur D and a rear derailleur ( not shown ) are operated by speed change levers to thereby move chain guides axially of the chain gears and switch a driving chain to desired ones of front chain gears FG and that of rear chain gears RG. The chain line of the driving chain may skew between the front chain gear FG and the rear chain gear RG, especially largely between a low speed front chain gear FG.sub.1 and a high speed rear chain gear RG.sub.1 or between a high speed front chain gear FG.sub.2 and a low speed rear chain gear RG.sub.2. In this case, the chain may strike the chain guide at its outer or inner plate to thereby generate noises. This often occurs when three front chain gears or six front chain gears are used.
In order to prevent such noise generation, a cyclist conventionally adjusts the speed change lever in position when operated to interrupt the continuation of noises.
Such conventional method is troublesome for the cyclist because the lever should be adjusted each time noises are generated. Also, it is impossible for the front derailleur to set its chain guide in position by operating the speed change lever for the front derailluer. The reason for the above is that even when a positioning mechanism for the front derailleur is provided at the speed change lever for the front derailleur, the aforesaid problem of noise generation has not been solved.